ACOUSTIC EMISSION - A NEW NONDESTRUCTIVE TESTING TOOL

A new approach to nondestructive testing is proposed which is centred around the concept of utilizing the transducer action of a flaw in a stress field. This situation results in local plastic deformation occurring in the vicinity of the flaw which in turn gives up energy in several different ways. Thermal emission, exo-electron emission and acoustic emission are the three primary forms that this energy takes upon release. The first two of these are mentioned only briefly as challenging new areas of research, while the remainder of this report is devoted to the subject of acoustic emission. It is shown that acoustic emission from unflawed tensile specimens can be treated from a dislocation dynamics approach. A very good correlation between the acoustic emission and a proposed theoretical model for mobile dislocation density as a function of plastic strain is shown for aluminum. A previously developed theoretical model for the plastic volume around a sharp crack in an elastic stress field predicted that the summation of acoustic emission should vary as the fourth power of the stress intensity factor at the crack tip. Experimental data from 7075-T6 aluminum is presented and agrees well with this model. It is further shown that acoustic emission data from flawed specimens, interpreted from a fracture mechanics viewpoint, can find direct application for nondestructive quality assurance tests on engineering structures. © 1969.